Here's a job control conundrum for you.

[Steven W. Orr]

On Wednesday, Apr 11th 2007 at 14:17 -0400, quoth Ben Scott:

=>On 4/11/07, Steven W. Orr <steveo at syslang.net> wrote:
=>> BTW, it turns out that killall -1 alpine from another window *is*
=>> effective.
=>
=> That almost sounds like killall is refusing to send the signal to
=>your process group as a "safety measure" kind of thing, i.e., don't
=>let the user kill himself.  The thing is, I've killed myself with
=>killall before, so that's not consistent.  Hrmmmm.
=>
=>> The --verbose shows that the kill(2) call did in fact not fail and that
=>> the process was delivered.
=>
=> So much for that theory.
=>
=> Hmmm, one correction, though: That shows the signal was *sent*.  You
=>need to use "--wait" to have killall wait and tell you if/when the
=>signal was *received*.

--wait doesn't return if the signal is received. There's no delay between 
the send and receive of a signal. --wait will loop around looking to see 
if the process actually disappears. The exit status of kill(2) is the 
indicator of whethr the signal was delivered.

=>
=>[various interesting commands]
=>> The fg then only prints out the name of the process but nothing happens.
=>
=> Hmmm.  Maybe a process cannot receive a signal when it is stopped?
=>I seem to recall that's the behavior.  You have to wake it up, then
=>the signals get delivered.  So when killall sends SIGHUP or SIGKILL,
=>the process doesn't get it until you wake it up, at which point it
=>gets delivered, and "alpine" promptly complies by exiting.

This is why I think it may be a bug in alpine. signal(2) can only handle 
one signal at a time. sigaction(2) will allow signals to stack up.

=> So why does "kill -1" work?  Well, kill is a shell built-in.  Maybe
=>it is aware of job status in your shell, and "helps" you by sending
=>SIGCONT to wake it up.

Naaa ;-)

=> Of course, this doesn't explain why a different shell's invocation
=>does work.  But I think this might be an avenue of exploration worth
=>following for a bit.  So, what happens if, instead of using the
=>shell's built-in kill, you do:
=>
=>	/bin/kill -1 $PID_OF_ALPINE

It's a mystery... ;-)

-- 
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steveo at syslang.net